1. Field of the Invention
The present invention relates to test instruments, and more particularly, to a test system based on a micro controller for digital control of the testing of a cathode ray tube (CRT) and various peripheral components thereof.
2. Description of the Prior Art
Cathode ray tube (CRT) is a display device widely used on oscilloscopes, computer monitors, TV, HDTV (high-definition TV), direct view and projection screens, and the like, for displaying traces, patterns, or pictures. A CRT comprises essentially a fluorescent screen, at least an electron gun (cathode) for emitting a beam of electrons, a heater for heating the cathode, a plurality of grids for controlling the flow of the electron beam from the cathode to the screen, a variety of coils for adjusting the focusing and positioning of the electron beam on the screen, and an anode disposed on the screen to attract the electron beam from the cathode to the screen.
For a monochrome CRT, there needs only one electron gun, whereas for a color CRT at least three electrons guns are needed, respectively for the red (R), green (G), and blue (B) channels. The plurality of grids used in the CRT are customarily referred to as G1, G2, and G3 in the industry. For high-resolution application, an additional grid G3-2 for fine focusing purpose is provided.
Further, the variety of coils in the CRT include essentially at least a horizontal deflection coil, a vertical deflection coil, a degaussing coil, a convergence coil, a rotation coil, and a purity coil. Besides these, there are provided other various peripheral components and controls on the CRT, including a video amplifier for amplifying the video signal to be displayed on the CRT screen, a tuning capacitor for the deflection yoke, S capacitors, and so on. All the aforementioned components and controls are conventional parts for building CRTs, which are well known to those skilled in the art of CRT design so that structural and functional description thereof will not be further detailed.
In the production process of a CRT and its peripheral components, front of screen performance of geometry color purity, rotor convergence, focus, and stray emission are essential operation and performance characteristics that nut be tested and adjusted. A test system for testing these CRT operation and performance characteristics must provide various voltages to the electrodes (cathode, grids, anode), heater, coils, video amplifier, degauss controller, and others.
Corventional CRT test systems consist of a collection of analog test instruments, each used for the testing of a particular operation and performance characteristic of the CRT. To operate these analog test instruments, the conventional CRT test systems are provided with a plurality of variable resistors, mechanical switches, and relays, which are used for control setting of each specific requirement such as setting a grid voltage or a defection center offset. Overall system control capability is lack in the conventional test systems. Among many control settings needed for the conventional test systems, for instances, Six control knobs are needed for testing a color CRT so as to set the bias and gain for each of the three electron guns. Moreover, over eight control knobs are needed to set geometry (vertical and horizontal), linearity, phase, size, pincushion, trapezoid, and raster centering.
Changing settings on the conventional CRT test systems is a very time-consuming and laborious work for the operator since there are so many parameters that must be entered manually. Certain settings can only be performed with the system power being turned off for example the deflection coil tuning capacitor setting the test system setting process is further aggravated since the operator must turn the system power off when changing the setting and then turn the power on to visually check the effects for several times.
Another drawback of the conventional test systems is that, since the control knobs are provided on the front panel, prescribed setting could be inadvertently changed by the operator if the operator accidentally touches anyone of the control knobs. Even worse, in the event of such an inadvertent change of the setting, the conventional test systems is unable to detect the faulty sting, which could cause-production quality drifts and system down time.
During the CRT production process, critical faults such as yoke winding shorts and high voltage arcing are common. Analog systems only have hardware protection circuit that may protect the instrument but still subject tee hardware to these abnormal conditions until the operator remove it. Over time, abnormal stress on the hardware will contribute to its shortened life. Once under fault condition, the conventional test system which is based on analog test instruments has only limited capabilities to convey the fault, fault diagnostics, and fault isolation messages to the operator.
Furthermore, for a multisync computer monitors, the testing and adjustment of the CRT thereon should be performed at various frequencies. However, an automatic multiple frequency operation is presently still not available on conventional CRT test systems. Using the conventional CRT test system which is based on analog test instruments, the operator must shut down the system and readjust quite a number of control knobs before a different frequency setting cm be used, which is a very inconvenient and time-consuming procedure.